R-T-B sintered magnets (where R is at least one element selected from among rare earth elements including Y, T is a transition element and B is boron) are used in a variety of electrical devices for their excellent magnetic properties.
Residual flux density (Br) and coercive force (HcJ) are generally used as indices of the magnetic properties of magnets. It is known that the HcJ value can be increased in an R-T-B sintered magnet by using Dy (dysprosium) as part of the rare earth element.
Such an R-T-B sintered magnet is fabricated by a common powder metallurgy process, and its cross-sectional structure is typically a structure such as shown in FIG. 2. Specifically, the R-T-B sintered magnet 100 comprises crystal grains 120 comprising an R2T14B phase as the main crystal phase (main phase), and grain boundary regions 140 present at the grain boundaries. A phase with a higher R content than the R2T14B phase is present at these grain boundary regions 140.
In order to increase the HcJ value of the R-T-B sintered magnet 100, it is effective to micronize the crystal grains 120. In order to micronize the crystal grains 120, it is necessary to micronize the particle diameter of the alloy powder used as starting material. When micronized alloy powder is used, however, the phase with a higher R content than the R2T14B phase tends to segregate during sintering, and it is difficult to sufficiently increase the HcJ value. For this reason it has been proposed, in PTL 1 for example, to limit the triple point mean area and the standard deviation of the area distribution to no greater than prescribed values, in order to avoid segregation of the phase with a higher R content than the R2T14B phase.